Wee gluons and their big role in crea2ng the ho3est ma3er on earth. Raju Venugopalan BNL

Transcription

1 Wee gluons and their big role in crea2ng the ho3est ma3er on earth Raju Venugopalan BNL Symposium, Sea3le, July 1 2, 2010

2 Quantum Chromodynamics (QCD) QCD nearly perfect fundamental quantum theory of quark and gluon fields (F.Wilczek, hep ph/ ) Theory is rich in symmetries: i ii i) Gauge color symmetry: unbroken but confined ii) Global chiral symmetry: exact for massless quarks iii) Baryon number and axial charge (m=0) are conserved iv) Scale invariance of quark (m=0) and gluon fields v) Discrete C,P & T symmetries Chiral, Axial, Scale and (in principle) P &T broken by vacuum/quantum effects emergent phenomena What happens at finite temperature & density? iii

3 QCD: structure & consequences Asympto2c freedom: S: Coupling strength of gluons weaker Gross, Wilczek, Politzer (1973) at short separa2on C: Super dense & super hot QCD ma3er is weakly coupled gas of quarks & gluons Collins Perry (1975); Cabibo Parisi (1975) Infrared slavery: Wilson (1974), Polyakov, S: Linear growth of sta2c quark an2 quark poten2al at large separa2on intui2ve picture of confinement C: QCD ma3er is strongly interac2ng at lower temp. & density Rich QCD Phase Diagram (Broken) Chiral symmetry S: spontaneously generated Chiral condensate C: Chiral symmetry restored at finite T Nambu Goldstone

4 QCD : brief pre history From E. Fermi: Notes on Thermodynamics and Sta2s2cs (1953) Ma3er in unusual condi2ons Hagedorn (1965) Lee Wick ma3er (1974) Collins Perry/Cabibbo Parisi (1975) Neutron Stars Quark Gluon Plasma (QGP) Shuryak (1978) Big Bang RHIC

5 Standard model of HI Collisions Color Glass Condensates Initial Singularity Glasma sqgp - perfect fluid! Hadron Gas t Though broad outlines could be guessed, current understanding far beyond anything anticipated when RHIC was proposed Solidify, Improve, Falsify?

6 Gluon Satura2on in a nucleus: classical coherence from quantum fluctua2ons Wee parton fluctuations time dilated on strong interaction time scales Parton Density The gluon density saturates at a maximal value of ~ 1/α S gluon satura2on Large occupa2on # => classical color fields 1/Q S 2 Parton momentum fraction / Proton momentum fraction

7 Many body high energy QCD: The Color Glass Condensate QCD framework to understand strongly correlated wee gluons in nuclei and their evolu2on with energy Dynamics characterized primarily by one universal semi hard scale the satura2on scale Q A S resolution Physics highly non perturba2ve, but can be described in weak coupling novel regime of QCD Powerful analogy to reac2on diffusion processes in sta2s2cal mechanics nuclear size energy

8 Evidence for RHIC? Rich Deuteron+Gold physics program Δφ= (near 0 side) Δφ= (away π side) CGC estimates for A+A bulk # s and trends Away side parton randomized by strong color field (rad )

9 Standard model of HI Collisions Color Glass Condensates Initial Singularity Glasma sqgp - perfect fluid! Hadron Gas t Glasma (\Glahs-maa\): Noun: non-equilibrium matter between Color Glass Condensate (CGC)& Quark Gluon Plasma (QGP)

10 The big role of wee glue What is the role of wee partons? How do the wee partons interact and produce glue? Can it be understood ab initio in QCD? Bj, DESY lectures (1975)

11 Classical features of the Glasma Solu2ons of Yang Mills equa2ons produce (nearly) boost invariant gluon field configura2ons: Glasma flux tubes Lumpy gluon fields are color screened in transverse plane over distances ~ 1/Q S Nega2ve Binomial mul2plicity distribu2on. Glasma flux tubes have non trivial longitudinal color E & B fields at early 2mes generate Chern Simons topological charge

12 The Ridge: Glasma flux tubes+ Radial flow Δφ Au+Au 200 GeV, 0-30% PHOBOS 1 Ntrig p+p d2nch dδφdδη 0-5% ry limina Pre STAR A+A Long range rapidity correla2ons are sensi2ve to Glasma dynamics at early 2mes Glasma flux tubes provide the long range rapidity correla2on Radial ( Hubble ) flow of the tubes provides the azimuthal collima2on

13 Chiral Magne2c Effect: Local strong parity viola2on L or B N CS = Topological fluctuations -sphaleron transitions in Glasma -as in EW baryogenesis External (QED) magnetic field Effect most significant, for transitions at early times = STAR Preliminary Chiral magnetic effect Possible experimental signal of charge separation 13

14 Standard model of HI Collisions Color Glass Condensates Initial Singularity Glasma sqgp - perfect fluid! Hadron Gas t Thermaliza2on of Glasma s2ll not understood Fast isotropiza2on may occur due to instability induced field amplifica2on very analogous to prehea2ng phenomenon in infla2onary cosmology Glasma provides ini2al condi2ons for hydrodynamic flow

15 Strong flow = (nearly) ideal hydrodynamics dn dy p dp dφ = 1 dn (1 + 2 v 2 (p ) cos 2(φ Ψ RP )+ ) 2π dy p dp Spatial anisotropy v 2 measures how efficiently hot ma3er converts spa2al anisotropies to momentum anisotropy most efficient way is hydrodynamics v 2 at RHIC is large (Barbara Jacak s talk) hydro flow must set in early

16 Bjorken Hydrodynamics A perfect fluid at RHIC Viscous term smaller than ideal term for dε dτ = η ε + P ( ε + P 4 3 τ 1 τ η s η τ ) 1 τt << 1 From kine2c theory η s k B τ relax. τ quant. H 2 O 4 He 6 Li sqgp

17 AdS/CFT conjecture: AdS/CFT and the KSS bound Duality between strongly coupled N=4 supersymmetric Yang Mills theory at large coupling and Nc & classical 10 dimensional gravity in the background of D3 branes KSS bound: Classical absorp2on cross sec2on of a graviton with energy ω on a black brane σ(ω) = 8πG dtdx e iωt [T xy (t, x),t xy (0, 0)] ω From Kubo: η = σ(0) 16πG Theorem: σ(0) = a a 4G where a= area of black brane From Beckenstein: s = Puyng it all together: η s k B 1 4π

18 η/s and viscous RHIC η/s from comparisons of viscous hydro codes to RHIC data suggest it nearly saturates the KSS bound perfect fluid Viscosity from perturba2ve es2mates Quan2ta2ve value quite sensi2ve to ini2al condi2ons Glasma! is significantly larger Probably safe to say its lower than any fluid with possible excep2on of cold 6 Li atoms in the unitarity limit (Feshbach resonance)

19 Perfect fluidity without thermaliza2on? Leading contribu2on to quantum evolu2on of T μν can be re expressed as classical evolu2on averaged over ensemble of quantum fluctua2ons T µν resum. [A] = [da] G[a] T µν LO [A + a] ! 4 potential, longitudinal expansion T 00 / 3 T zz w/o fluctuations T zz with fluctuations " -4/3 i) Phase decoherence leads rapidly to perfect fluidity => large flow 10 1 ii) These quantum fluctua2ons may also be responsible for sphaleron transi2ons giving rise to the Chiral Magne2c Effect time

20 Hard Probes of the sqgp High p T (>> T) hadrons, heavy mesons (charm and beauty), J/ψ and Upsilon, hard photons and JETS

21 dt d z Q z D Q x Q x dx dx dp d E c abc a B b a A a b a σ π µ µ φ µ φ σ π ˆ ),, ( ),, ( ),, ( 2 / 2 / 2 / = φ a/a φ b/b A B ab σˆ D(z) The pp Benchmark pqcd works excep2onally RHIC to fairly low p T

22 Parton energy loss ˆq Ideal gas Wide dispersion in theory es2mates de dz = α SN c 4 p 2 =ˆqL p 2 Characterizes proper2es of hot medium

23 Weak versus Strong coupling in the sqgp Weak coupling approaches fit the jet quenching data however, computa2ons are not under control & large heavy quark energy loss is difficult to reconcile Large energy loss for light and heavy quarks natural in AdS/CFT approach But no jets in AdS! Synchrotron radia2on in AdS may be more like in QCD collimated jets Lots of exci2ng ideas but no clear picture of transport in sqgp Close Window

24 Outlook We now have a standard model of HI collisions with unan2cipated features like the CGC, the Glasma & sqgp The sqgp produced at RHIC may be the most perfect fluid in nature Many approaches to understand and quan2fy the proper2es of the sqgp but no consensus yet Nearly everything said here may have to be revised once data from the LHC Pb+Pb become available

25 THE END THANK YOU!

26 Strong flow = (nearly) ideal hydrodynamics QCD Hydrodynamics = low energy effec2ve theory of QCD valid at large distances (L >> λ mfp ) Rela2vis2c hydrodynamics: Conserva2on laws µ T µν =0 µ j µ =0 Cons2tu2ve equa2ons: T µν =(ε + P )U µ U ν + Pg µν +τ µν j µ = nu µ +ν µ Dissipa2ve terms: τ ij = η ( i U j + j U i 23 ) δij U ζδ ij U Shear viscosity ν i = σt i ( µ T ) Conduc2vity (diffusion) Bulk viscosity